RESEARCH MONOGRAPH · KDC-MN-261

Ostarine (MK-2866)

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 3 min read

Our opinion on this compound

61/100

The most-studied SARM with the cleanest data, and that bar is still lower than people pretend

Ostarine (also enobosarm, GTx-024) is the SARM with the most respectable clinical development history, which is faint praise in a class where most candidates never made it past phase 2. GTx ran it through trials for cancer cachexia, stress urinary incontinence in women, and breast cancer-related muscle wasting. The cachexia program got the furthest, with phase 3 data showing real but smaller-than-hoped lean mass gains and a co-primary endpoint miss on physical function that killed the indication.

The mechanism is reasonably well-mapped for the class. Ostarine is a non-steroidal AR agonist with preferential tissue selectivity for muscle and bone over prostate and other reproductive tissues, driven by differences in coactivator recruitment and tissue-specific co-regulator expression. The selectivity isnt absolute and at higher exposures the prostate-sparing claim weakens substantially. AR is AR.

What we like is that ostarine has more controlled human pharmacokinetic and safety data than basically any other SARM. Suppression of LH, FSH, and testosterone is dose-dependent and reversible in most reported cohorts, the half-life is in the 24-hour range which makes once-daily dosing reasonable, and the hepatic transaminase signal is real but generally mild at the clinical doses tested.

What we dont like is the gap between trial doses and what the gray-market consumer scene has been using. The 3 mg per day dose used in most GTx trials is not the 25-to-50 mg per day that crept into the bodybuilding scene, and the safety profile at those higher exposures includes more substantial HPG suppression, dyslipidemia, and rare but documented hepatotoxicity. The WADA banning in 2008 reflects real performance-enhancement signal, not anti-doping overreach.

Sourcing is the persistent problem. Ostarine has been the most counterfeited SARM in the gray market, with multiple FDA warning letters about products mislabeled or contaminated with other SARMs, prohormones, or unrelated PEDs. For research-grade material the HPLC purity and NMR identity confirmation matter, and even legitimate research suppliers vary in QC consistency.

Honest take: best-studied SARM, real pharmacology, partial clinical signal that fell short of approval, persistent sourcing risks, abuse outside the research context inflated the bad press. For research purposes the data is genuinely useful as a reference compound for AR tissue selectivity work. Just dont confuse trial doses with what's in the supplement scene.

Evidence: 65
Mechanism: 72
Reliability: 68
Safety: 55
Sourcing: 50
Value: 60
Signal: 65
Staying power: 55

Plain-language summary Intrigue 70 / 100

Ostarine (MK-2866, enobosarm) is the most-studied selective androgen receptor modulator (SARM), a class designed to deliver the muscle and bone effects of anabolic steroids without the prostate, liver, and hair-loss side effects. It binds the same androgen receptor as testosterone but produces full activity in muscle and bone while doing little in prostate tissue, owing to differences in receptor partners across tissues. Trial doses of 1 to 3 mg in the published literature produced measurable lean-mass gains in cancer cachexia and elderly populations. It never won FDA approval (failed primary endpoints in phase 3 cachexia trials), but it is the most thoroughly characterized SARM in humans and is widely used recreationally at supraclinical doses. WADA-banned. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Selective androgen receptor modulator (non-steroidal)

A selective androgen receptor modulator developed for cachexia and muscle wasting; the prototype SARM and the most thoroughly characterized in human trials.

Abstract

Ostarine (Enobosarm, MK-2866, GTx-024; CAS 841205-47-8; molecular formula C19H14F3N3O3; molecular weight 389.33) is a selective androgen receptor modulator (SARM) developed at GTx Inc. (later licensed to Merck). The compound is a non-steroidal aryl propionamide that binds the androgen receptor (AR) with tissue-selective agonism: full agonist activity in skeletal muscle and bone, partial or absent activity in prostate and sebaceous glands. The selectivity arises from tissue-specific differences in AR coactivator and corepressor expression and from differential conformational induction by non-steroidal versus steroidal ligands. Phase 2 trials in cancer cachexia and stress urinary incontinence demonstrated lean body mass gains and bone density improvements, but a definitive phase 3 trial in cancer cachexia (POWER) failed to meet primary endpoints in 2013. The compound retains significant academic interest as a SARM prototype and is widely used recreationally (banned by WADA in sport) despite no regulatory approval. Plasma half-life is approximately 24 hours; oral bioavailability is high. The principal safety concerns are hepatic enzyme elevation and HPG axis suppression at supratherapeutic doses.

Mechanism of action

Non-steroidal SARM with tissue-selective AR agonism (full agonist in muscle/bone; weak in prostate/sebaceous glands). Mechanism via differential conformation and coactivator recruitment.

Reported research dose ranges

Trial doses 1 to 3 mg in the published literature; recreational use commonly 10 to 25 mg.

References

Dalton JT, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women. J Cachexia Sarcopenia Muscle 2011.
Crawford J, et al. Study design and rationale for the phase 3 clinical development program of enobosarm. Expert Opin Investig Drugs 2017.
Mohler ML, et al. Nonsteroidal selective androgen receptor modulators (SARMs). J Med Chem 2009.

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KDC-MN-261

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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Ostarine (MK-2866)

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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